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#![cfg(feature = "std")]
#[macro_use]
extern crate custom_error;
use std::{fs::File, io, io::ErrorKind, io::Read, num::ParseIntError, result::Result};
custom_error! {
OpenFileError
NotFound{filename: String} = "Tried to open '{filename}', but it doesn't exist",
Other = "An unknown I/O error occured.",
}
/// Opens a file with a verbose error on failure
fn open_file_verbose(filename: &str) -> Result<File, OpenFileError> {
File::open(filename).map_err(|e| match e.kind() {
ErrorKind::NotFound => OpenFileError::NotFound {
filename: filename.to_string(),
},
_ => OpenFileError::Other,
})
}
custom_error! {FileParseError
Open{source: OpenFileError} = @{ source }, // Chained custom error
Io{source: io::Error} = "I/O error",
Format{source: ParseIntError} = "the file does not contain a valid integer",
TooLarge{value:u8} = "the number in the file ({value}) is too large"
}
fn parse_hex_file(filename: &str) -> Result<u8, FileParseError> {
let mut contents = String::new();
// The '?' notation can convert from generic errors to our custom error type
open_file_verbose(filename)?.read_to_string(&mut contents)?;
let value = u8::from_str_radix(&contents, 16)?;
if value > 42 {
Err(FileParseError::TooLarge { value })
} else {
Ok(value)
}
}
#[test]
fn main() {
let parse_result = parse_hex_file("/i'm not a file/");
assert_eq!(
"Tried to open '/i'm not a file/', but it doesn't exist",
parse_result.unwrap_err().to_string()
);
}
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